EP3183846B1 - Subscriber station for a bus system, and method for checking the correctness of a message - Google Patents

Description

Technical area

The present invention relates to a subscriber station for a bus system and a method for checking the correctness of a message sent in the bus system, the subscriber station and the method enabling the configuration of an initialization value for a checksum generator.

State of the art

US2004 / 081079 A1 shows a communication controller with a bus guardian monitoring the cyclic timed flexray access scheme applied to the bus. With a priori knowledge, the bus guardian can distinguish between a permitted deviation and a prohibited deviation.

The CAN bus system has gained wide acceptance for communication between sensors and ECUs. For example, it is used in automobiles. The CAN bus system transmits messages using the CAN protocol as described in ISO11898. In particular, automotive bus systems are continually evolving toward higher bandwidth, lower latency, and more rigorous real-time capability. More recently, techniques have been proposed for this, such as CAN FD, in which messages conforming to the specification "CAN with Flexible Data Rate,

Specification Version 1.0 "(source http://www.semiconductors.bosch.de) or corresponding to the revision ISO11898-1 (currently available as ISO11898-1 CD), etc. With such techniques, the maximum possible data rate Increasing the speed of data fields beyond 1 Mbps, such as CAN FD frames or CAN FD messages.

The extension of the CAN standard has been supplemented by primarily functional supplements, such as TTCAN, recently with CAN FD especially with regard to the possible (higher) data rate and the usable data packet size extended, the original CAN properties were obtained especially in the form of arbitration.

Problems currently exist in calculating the checksum of a CAN FD frame when the identifier of the CAN FD frame begins with four dominant bits. These four dominant bits together with a dominant start bit of the CAN FD frame, also called start-of-frame bit, form a stuff condition, according to which a recessive stuff bit (stuffing bit) is inserted between the fourth and fifth bits of the identifier. In this case, if locally in a receiver of the CAN FD frame, the dominant initial bit of the CAN FD frame is overwritten with a recessive bit, the receiver of the CAN FD frame interprets the first dominant bit of the identifier as the initial bit of the frame. Since there is no stuff condition due to the received recessive stuff bit in the receiver, the receiver will accept the recessive stuff bit as the fourth bit of the identifier. The following bit will be accepted as the fifth bit of the identifier and the receiver will be back in phase with the transmitter. However, in this case, the modified fourth bit of the identifier is not recognized at the checksum at the end of the CAN FD frame. For example, an identifier 0x001 sent by the transmitter is received by the receiver as 0x081. This applies to both the 11-bit identifier and the 29-bit identifier in CAN FD.

Disclosure of the invention

Therefore, it is an object of the present invention to provide a subscriber station for a bus system and a method for checking the correctness of a message, which solve the aforementioned problems. In particular, a subscriber station for a bus system and a method for checking the correctness of a message are to be provided which can reliably detect bit errors of a message sent or received in the bus system. The object is achieved by a subscriber station for a bus system with the features of claim 1. The subscriber station comprises a communication control device for generating or reading at least one message for / from at least one further subscriber station of the bus system, in which an exclusive, collision-free access of a subscriber station to a bus line of the bus system is ensured at least temporarily, a checksum generator for generating a checksum A message for detecting bit errors of the message and a configuration register for specifying with which initialization value the checksum generator is to be preloaded to start the message, wherein the initialization value is stored in the configuration register, the initialization value of software as needed prior to beginning communication in the bus system will be changed.

With the subscriber station, it is possible to change a previously fixed initialization value for a checksum generator as needed or to make configurable. This allows the subscriber station, more precisely its checksum generator, to work both with the previous initialization value of "0x00000" and with a new initialization value yet to be determined. As a result, bit errors of a message of the bus system can be reliably detected by forming a checksum.

Due to the freely selectable specification of the initialization value for the checksum generator, the subscriber station can also be easily adapted to further developments in further developments of the message transmission standard. Even if it is decided, in particular for CAN FD, not to change the standard, a conformance test can be passed with the subscriber station. The subscriber station can then optionally also communicate with other, already existing CAN FD subscriber stations which use the currently defined initialization value.

Advantageous further embodiments of the subscriber station are specified in the dependent claims.

According to one embodiment, the configuration register may be configured as a rewritable memory.

According to a further embodiment, the configuration register may comprise at least one changeable configuration bit, and at least two initialization values as permanently stored values, wherein the at least one changeable configuration bit indicates with which of the at least two initialization values the checksum generator is to be preloaded to start the message.

It is conceivable that the subscriber station further comprises: another checksum generator for generating a checksum of the message to detect bit errors of the message, and another configuration register for specifying with which initialization value the further checksum generator is preloaded to start the message, the checksum generator for generating a checksum of a message having less than a predetermined number of data bytes and the further checksum generator configured to generate a checksum of a message having more than the predetermined number of data bytes. Here, the predetermined number of data bytes 16 may be.

In the subscriber station described above, the communication control device may comprise the configuration register and the further configuration register.

The at least one message may be a CAN FD message.

The subscriber station described above may be part of a bus system, which also comprises a parallel bus line and at least two subscriber stations, which are connected to one another via the bus line so that they can communicate with each other. In this case, at least one of the at least two subscriber stations is a subscriber station described above.

The above object is further achieved by a method for checking the accuracy of a message according to claim 9. Here is the To create or read a message with a communication control device of a subscriber station for / from at least one further subscriber station of the bus system, in which an exclusive, collision-free access of a subscriber station to a bus line of the bus system is ensured at least temporarily, the method comprising the steps of: storing an initialization value in a configuration register, wherein the initialization value is changed by a software as needed before the beginning of a communication in the bus system,
Specifying, with the configuration register, with which initialization value a checksum generator is preloaded to start the message, wherein the checksum generator is to calculate a checksum of the message to detect bit errors of the message.

The method offers the same advantages as previously mentioned with respect to the subscriber station.

Further possible implementations of the invention also include not explicitly mentioned combinations of features or embodiments described above or below with regard to the exemplary embodiments. The skilled person will also add individual aspects as improvements or additions to the respective basic form of the invention.

drawings

• Fig. 1 ein vereinfachtes Blockschaltbild eines Bussystems gemäß einem ersten Ausführungsbeispiel;
• Fig. 2 eine schematische Darstellung des Aufbaus einer Nachricht bei einem Bussystem gemäß dem ersten Ausführungsbeispiel;
• Fig. 3 eine Ansicht zur Veranschaulichung der Funktion eines Konfigurationsregisters des Bussystems gemäß dem ersten Ausführungsbeispiel;
• Fig. 4 ein vereinfachtes Blockschaltbild eines Bussystems gemäß einer Modifikation des ersten Ausführungsbeispiels; und
• Fig. 5 eine Ansicht zur Veranschaulichung der Funktion eines Konfigurationsregisters des Bussystems gemäß einem zweiten Ausführungsbeispiel.

The invention is described in more detail below with reference to the accompanying drawings and to exemplary embodiments. Show it:

• Fig. 1 a simplified block diagram of a bus system according to a first embodiment;
• Fig. 2 a schematic representation of the structure of a message in a bus system according to the first embodiment;
• Fig. 3 a view for illustrating the function of a configuration register of the bus system according to the first embodiment;
• Fig. 4 a simplified block diagram of a bus system according to a modification of the first embodiment; and
• Fig. 5 a view for illustrating the function of a configuration register of the bus system according to a second embodiment.

In the figures, identical or functionally identical elements are provided with the same reference numerals, unless stated otherwise.

Description of the embodiments

Fig. 1 shows a bus system 1, which may be, for example, a CAN bus system, a CAN FD bus system, etc. The bus system 1 can be used in a vehicle, in particular a motor vehicle, an aircraft, etc., or in the hospital, etc.

In Fig. 1 the bus system 1 has a plurality of subscriber stations 10, 20, 30, which are each connected to a bus line 40. Messages 3, 4 in the form of signals can be transmitted via the bus line 40 between the individual subscriber stations 10, 20, 30. The subscriber stations 10, 20, 30 may be, for example, control devices or display devices of a motor vehicle.

As in Fig. 1 subscriber station 10 has a communication control device 11, a checksum generator 12, a configuration register 13, and a transceiver 14. The subscriber station 20, on the other hand, has a communication control device 21 comprising a checksum generator 12 and a configuration register 13, and a transmission / Receiving device 14. The subscriber station 30 has a communication control device 11, a checksum generator 12 and a transmitting / receiving device 14. The transmitting / receiving devices 14 of the subscriber stations 10, 20, 30 are each directly connected to the bus line 40, even if this is in Fig. 1 not shown.

As in Fig. 1 shown, the subscriber stations 10, 20, 30 each have a checksum generator 12. The subscriber stations 10, 20 also each have a configuration register 13. In the subscriber station 20, the checksum generator 12 and the configuration register 13 are part of the communication control device 21. In the subscriber station 30, no configuration register 13 is present, since the initialization value with a fixed initialization value or initialization vector, for example "0x00000", is fixed in the bus system 1 before communication begins is predetermined and unchangeable. Here, the prefix "0x" stands for the hexadecimal representation of the initialization value, hexadecimal 0x0 in binary "0000" or hexadecimal "0xA" in binary "1010". The communication control device 21 of the subscriber station 20 is otherwise the same as the communication control device 11 of the subscriber station 10.

The communication control device 11 serves to control communication of the respective subscriber station 10, 20, 30 via the bus line 40 with another subscriber station of the subscriber stations 10, 20, 30 connected to the bus line 40. The checksum generator 12 is used to calculate a checksum, for example a CRC. Checksum (CRC = cyclic redundancy check) over predetermined bits of the messages 3, 4. The configuration register 13 stores before the start of communication in the bus system 1 an initialization value, as described in more detail below. The communication controller 11 may be implemented like a conventional CAN or CAN FD controller. The transceiver 14 may be implemented like a conventional CAN or CAN FD transceiver.

With the two subscriber stations 20, 30, a formation and then transmission of messages 3 can be realized with CAN FD or with higher data rates than CAN FD. By contrast, the subscriber station 10 corresponds to a conventional CAN or CAN FD subscriber station both in terms of its transmission and its reception functionality and transmits messages 4 according to the current CAN or CAN FD protocol.

Fig. 2 shows very schematically the structure of a message 3. Accordingly, the message 3, which is also referred to as a frame, a frame header 31, a data segment 32 and a checksum 33, which follows the frame end 34. The frame header 31 is located at the beginning of the message 3, the data segment 32 in the middle and the checksum 33 and the frame end 34 at the end of the message 3. The checksum 33 is generated or calculated by the checksum generator 12. A message 4 is structured in the same way as the message 3.

Fig. 3 illustrates that an initialization value 131 for the checksum generator 12 is stored in the configuration register 13. The initialization value 131 is arbitrarily changed by a software 51 as needed before the start of the communication in the bus system 1. Therefore, the configuration register 13 is configured as a rewritable memory. Thus, in contrast to the subscriber station 10, the subscriber stations 10, 20 have no fixed initialization value. The software 51 may be stored in an external microcontroller 50, which may be connected to the communication controller 11 and / or the communication controller 21. The microcontroller 50 may be part of the respective subscriber station 10, 20 or arranged externally thereof.

Fig. 4 shows a modification of the first embodiment. If checksums 33 of different lengths are calculated in the subscriber stations 10, 20, 30, for example a CRB checksum with 17 bits or a CRC checksum with 21 bits, which takes place in particular as a function of the length of the messages 3, 4, the subscriber stations 10, 20 for each of the lengths a separate checksum generator 12, 120. The same may apply to the subscriber station 30, even if this is in Fig. 4 not shown. For CAN FD, the subscriber stations 10, 20, 30 have a checksum generator 12 for a 17 bit CRC checksum calculated for a message 3 containing less than a predetermined number DN of data bytes in the data segment 32 (FIG. Fig. 2 ), such as 16 bytes. In addition, the subscriber stations 10, 20 have another checksum generator 120 for a 21-bit CRC checksum calculated for a message 3 that is more than the predetermined number DN of data bytes in the data segment 32 ( Fig. 2 ), such as 20 bytes. In this case, a configuration register 13, 130 with the corresponding initialization value 131 is also provided in the subscriber stations 10, 20 for each checksum generator 12, 120. In such a case, a fixed, unchangeable initialization value for the CRC checksum with 17 bits and a fixed, unchangeable initialization value for the 21-bit CRC checksum are provided in the subscriber station 30 in each case.

The present embodiment and its modification is particularly advantageous if the possible initialization values 131 are not or only partially known. In this case, the initialization values 131 can be arbitrarily set as needed.

Fig. 5 shows a configuration register 13 according to a second embodiment. Here, two different initialization values 131, 132 are permanently stored in the configuration register 13 or incorporated as constants. In order to select the respective initialization value 131, 132 for a checksum generator 12, the configuration register 13 has a configuration bit 133. The value of the configuration bit 133 is set by the microcontroller 50 or its software. Depending on the value of the configuration bit 133, the assigned initialization value 131, 132 is selected for the respective checksum generator 12. In this case, the at least one configuration bit 133 switches between the two different initialization values 131, 132.

The further configuration register 130 is executed in the same way as the configuration register 13 in the present exemplary embodiment.

Otherwise, the bus system according to the present embodiment is executed in the same manner as described in the first embodiment.

The present embodiment is advantageous if the possible initialization values 131, 132 are already known.

In a modification of the second embodiment, more than one configuration bit 133 may also be present. In this case, more than two initialization values 131, 132 may be permanently stored. In this case, more than two initialization values 131, 132 may be selected.

According to a third embodiment, the configuration register 13 is implemented as described in the first embodiment. In contrast, the second or further configuration register 130 is executed as described in the second embodiment. Otherwise, the bus system according to the present embodiment is executed in the same manner as described in the first embodiment.

All of the above-described embodiments of the bus system 1, the subscriber stations 10, 20, 30 and the method can be used individually or in all possible combinations. In particular, all the features of the previously described embodiments and / or their modifications can be combined as desired. In addition, the following modifications are conceivable, in particular.

The bus system 1 according to the exemplary embodiments described above is described on the basis of a bus system based on the CAN protocol. However, the bus system 1 according to the embodiments may be another type of communication network. It is advantageous, but not necessarily a prerequisite, that in the bus system 1, at least for certain periods of time, an exclusive, collision-free access of a subscriber station 10, 20, 30 to a common channel is ensured.

The bus system 1 according to the exemplary embodiments is in particular a CAN network or a TTCAN network or a CAN FD network.

The number and arrangement of the subscriber stations 10, 20, 30 in the bus system 1 of the embodiments is arbitrary. In particular, too only subscriber stations 10 or subscriber stations 20 etc. may be present in the bus system 1 of the embodiments.

Claims (9)

1. Subscriber station (10; 20) for a bus system (1), having

   - a communication control device (11; 21) for creating or reading at least one message (3) for/from at least one further subscriber station of the bus system (1), wherein the bus system (1) includes a bus line (40) and is designed such that access to the bus line by any participating subscriber station (10, 20, 30) is at least intermittently ensured as an exclusive, collision-free access,

   - a first checksum generator (12; 120) for generating a checksum (33) for the message (3) in order to detect bit errors in the message (3), and

   - a first configuration register (13; 130) for prescribing the initialization value (131; 131, 132) with which the first checksum generator (12; 120) is to be preloaded at the start of the message (3), wherein the subscriber station is adapted to store the initialization value (131; 131, 132) in the first configuration register (13; 130), and to be able to alter the initialization value (131; 131, 132) from a piece of software (51) as required before the beginning of a communication in the bus system (1).
2. Subscriber station (10; 20) according to Claim 1, wherein the first configuration register (13; 130) is configured as an overwritable memory.
3. Subscriber station (10; 20) according to Claim 1, wherein the first configuration register (13) has at least one alterable configuration bit (133), and at least two initialization values (131, 132) as permanently stored values,
   wherein the at least one alterable configuration bit (133) indicates that of the at least two initialization values (131, 132) with which the first checksum generator (12) is to be preloaded at the start of the message (3).
4. Subscriber station (10; 20) according to one of the preceding claims, also having a second checksum generator (120) for generating a checksum (33) for the message (3) in order to detect bit errors in the message (3), and a second configuration register (130) for prescribing the initialization value (131; 131, 132) with which the second checksum generator (120) is preloaded at the start of the message (3), wherein the first checksum generator (12, 120) is configured to generate a checksum that has fewer than a predetermined number (DN) of data bytes, and wherein the second checksum generator (120) is configured so that the checksum that it generates has more than the predetermined number (DN) of data bytes.
5. Subscriber station (10; 20) according to Claim 4, wherein the predetermined number (DN) of data bytes is 16.
6. Subscriber station (20) according to one of the preceding claims, wherein the communication control device (21) has the first configuration register (13) and the second configuration register (130).
7. Subscriber station (10; 20) according to one of the preceding claims, wherein the at least one message (3) is a CAN FD message.
8. Bus system (1) having
   a parallel bus line (40), and
   at least two subscriber stations (10, 20, 30) connected to one another via the parallel bus line (40) such that they can communicate with one another,
   wherein at least one of the at least two subscriber stations (10, 20, 30) is a subscriber station (10; 20) according to one of the preceding claims, and wherein the parallel bus line (40) is the bus line (40) .
9. Method for checking the correctness of a message (3) that can be created or read, using a communication control device (11; 21) of one subscriber station (10; 20), for/from at least one further subscriber station of the bus system (1), wherein the bus system (1) includes a bus line (40) and is designed such that access to the bus line by any participating subscriber station (10, 20, 30) is at least intermittently ensured as an exclusive, collision-free access, wherein the method has the following steps:

   - storing an initialization value (131; 131, 132) in a configuration register (13; 130),
   wherein the subscriber station is adapted to be able to alter the initialization value from a piece of software as required before the beginning of a communication in the bus system,

   - prescribing, using the configuration register (13; 130), the initialization value (131; 131, 132) with which a checksum generator (12; 120) is preloaded at the start of the message (3), wherein the checksum generator (12; 120) is adapted to calculate a checksum (33) for the message (3), and
   wherein the subscriber station is adapted to use the checksum to detect bit errors in the message (3).

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